1. Field of the Invention
The present invention relates to an engine speed controlling system capable of decreasing the engine speed for fuel economy during suspension of work in a construction machine such as a hydraulic shovel.
2. Description of the Prior Art
As this type of an engine speed controlling system, or a so-called auto-decelerating system, there has heretofore been known such a system as disclosed in Japanese Patent Publication No. 38561/85 wherein when a neutral condition of operating levers has been continued for a preset delay time, this condition is judged to be an operation suspended condition and the engine speed is decreased.
In an actual operation, however, a stand-by condition sometimes continues over the above delay time when a preset engine speed is to be maintained so that the operation can be restarted any time without being stopped. But the foregoing auto-decelerating system functions also in such a case against the operator's will and thus the operability thereof has been poor. The engine consumes a large amount of fuel particularly at the time of sudden rise from low speed, so if the control of slowdown (auto-deceleration) to acceleration against the operator's intention of continuing the work is repeated, the amount of fuel consumed will rather increase contrary to the desired purpose of fuel economy.
In order to eliminate such drawback there has been proposed such a system as disclosed in Japanese Patent Laid-Open No. 1837/86 wherein a grip sensor is attached to an operating lever to prevent the auto-decelerating function from being exhibited as long as the operator touches the operating lever even when the lever is in a neutral condition (in other words, to allow such function to be exhibited only when the operator releases his hand from the lever). However, whether the operator touches the operating lever or not is not always based on the his will. The operator may touch the lever or release his hand from the lever unconsciously, or any other person than the operator may touch the lever. Thus, the conventional system in question is disadvantageous in that the control is not always made exactly according to the operator's will.